The present invention relates to improvements in surface conditions of a rolling sliding member which comes in rolling or sliding contact with its mating face during use such as bearing ring, rolling element and retainer constituting a rolling bearing or cam follower. More particularly, the present invention can exert a great effect particularly when used in an application which is subject to great load and hence smearing or seizing such as roll neck bearing for steel rolling mill and bearing for railway vehicle.
For the purpose of preventing rust or improving lubricating properties in the initial stage of operation, it is commonly practiced to provide a formed film of manganese phosphate on the surface of various mechanical parts made of an iron-based metal which makes displacement relative to the surface of its mating member during use, e.g., sliding surface thereof. However, formation not only causes the rise in surface roughness but also worsens the dimensional accuracy by the thickness of the formed film. The rise in surface roughness and the deterioration of dimensional accuracy cause not only the rise in torque or calorific value in the initial stage of operation but also the deterioration of rotary properties. Therefore, it is commonly practiced to control the kind, concentration and other factors of the forming solution to be used so that the formed film can be reduced in thickness and formed by dense grains.
The process for the production of a chemically formed film of manganese phosphate will be generally described hereinafter. In some detail, when a rolling sliding member made of an iron-based metal is dipped in an aqueous solution of manganese phosphate, the aqueous solution of manganese phosphate undergoes primary dissociation to produce free phosphoric acid that dissolves iron on the surface of the substrate metal of the rolling sliding member to decrease the hydrogen ion concentration on the metal surface. While the equilibrium of dissociation of the foregoing aqueous solution of manganese phosphate moves over the surface of the substrate metal constituting the foregoing rolling sliding member, an insoluble manganese phosphate crystal is deposited on the surface of the substrate metal.
The manganese phosphate crystal thus deposited on the surface of the substrate metal is manganese and iron. The particle diameter of the crystal and the thickness and roughness of the deposit are affected by the components of the compound. Accordingly, the particle diameter of the manganese phosphate crystal deposited on the surface of the substrate metal increases to increase the surface roughness of the deposit depending on the composition of the foregoing aqueous solution of manganese phosphate which is a forming solution. When the surface roughness of the deposit thus increases, the substantial contact area of the surface of the rolling sliding member with the surface of its mating member decreases. In addition, protrusion interference between crystal particles causes early peeling of the formed film during operation.
The surface of the substrate metal which has been exposed after the peeling of the formed film has a raised surface roughness because iron has been dissolved during the process of production of the formed film. Therefore, after the peeling of the formed film, minute protrusions present on the rough surface of the exposed iron-based metal undergo interference with each other (collision of protrusions present on the surface of a pair of members which make displacement relative to each other), causing early damage such as smearing on the metal surface that can result in serious damages such as seizing in some extreme cases.
Under these circumstances, JP-A-6-159371 (The term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) discloses a technique which comprises controlling the composition and concentration of the forming solution to make the surface roughness of a formed substrate metal as large as twice or less that of an unformed substrate metal. In accordance with this technique, even after the formed film has been peeled to cause the substrate metal to be exposed, an oil film can be formed between the metal surfaces to prevent the occurrence of serious damages such as early peeling and seizing on the metal surface.
The inner ring, outer ring and rolling elements constituting a rolling bearing are rolling sliding members for which the present invention is intended. The provision of a formed film such as manganese phosphate film on the surface of the inner ring, outer ring and rolling elements has heretofore been practiced for rolling bearing for roll neck as shown in FIGS. 9 and 10. A roll for rolling a metal comprises a column portion called roll neck provided in the central part of the both axial end faces. The column portion is supported by a rolling bearing as shown in FIGS. 9 and 10 in such an arrangement that it can be freely rotated with respect to a fixed supporting device. The rotary bearing device for roll neck shown in FIGS. 9 and 10 will be firstly described. The roll neck 2 provided in the central part of the both axial end faces of the roll 1 is rotably supported inside the housing 3 by a double-row tapered roller bearing unit 4. The double-row tapered roller bearing unit 4 comprises a plurality of tapered rollers 9, 9 provided between inner ring races 6, 6 provided on the outer surface of innre rings 5, 5 externally fitted onto the roll neck 2 and outer ring races 8, 8 provided on the inner surface of outer rings 7a, 7b internally fitted into the housing 3.
The roll 1 which is rotably supported by the foregoing bearing device is rotated at a rate of from 1,000 to 1,800 minxe2x88x921 (r.p.m.) during the operation of the rolling apparatus. Accordingly, it is necessary that the bearing device comprise a grease enclosed therein so that it can be lubricated during the operation of the rolling apparatus. At the same time, it is necessary that the metal material to be rolled be sprayed with cooling water to prevent the temperature rise accompanied by rolling. Therefore, the bearing device is provided with a sealing device for preventing the lubricant from leaking out as well as preventing foreign matters such as the cooling water from entering into the interior of the bearing device. As the rolling bearing for bearing the roll neck 2 there may be used a cylindrical roller bearing besides the tapered roller bearing as shown in the drawings.
Anyway, the rolling bearing for rotably bearing the roll neck 2 of the rolling machine is used in severe atmospheres such as high temperature, high load and varying load. Further, as the rolling machine operates, foreign matters such as the cooling water and rolling scale often enter into the interior of the rolling bearing for bearing roll neck to cause mislubrication. The life of the rolling bearing for bearing roll neck which is subject to such severe conditions during use is not the rolling fatigue life as seen in ordinary rolling bearings. It is affected by the fatigue accompanying surface damages due to mislubrication or sliding friction. In other words, the foregoing rolling bearing often reaches its life due to fatigue accompanying surface damages before reaching rolling fatigue life.
In order to prevent the reduction of the life of rolling bearing forbearing roll neck due to this cause, it has heretofore been practiced to properly design the material and shape of the various members constituting this rolling bearing or the composition of the lubricant to be enclosed in this rolling bearing. Further, it has heretofore been practiced to subject the surface of various members constituting the rolling bearing such as inner ring race 6, outer ring race 8 and rolling surface of tapered rollers 9, 9 to formation to for mamanganese phosphate film or baked molybdenum disulfide film thereon.
The foregoing formation makes it possible to prevent rust of various members constituting the foregoing rolling bearing for bearing roll neck (inner ring 5, outer ring 7a, 7b, rolling elements such as tapered rollers 9, 9) and scoring on the portion at which the inner surface of the inner ring 5 engages the outer surface of the roll neck 2. In other words, by forming a formed film such as manganese phosphate film or baked molybdenum disulfide film on the surface of various members constituting a rolling bearing which is subject to severe conditions during use as mentioned above, so-called metal contact involving direct contact of substrate metal of the various members can be prevented. At the same time, these members can be prevented from being rust.
In accordance with the technique described in above cited JP-A-6-159371, the durability of a rolling sliding member made of an iron-based metal can be improved to some extent. More improvements have been desired to improve further the durability of the rolling sliding member.
For example, in the case of the rolling bearing forbearing roll neck as described above, by forming a formed film on the surface of various members constituting the rolling bearing, the damage and rust of the contact area can be prevented as mentioned above. However, the constituent members which have been merely subjected to formation cannot necessarily exert a sufficient effect. This reason will be described hereinafter. The foregoing formed film can be early peeled in a severe operating atmosphere. In accordance with the conventional treatment involving mere formation, the substrate metal covered by a formed film has a rough surface having a high surface roughness. This is because the surface of the substrate metal is eluted with a solvent during the process of production of the formed film by formation. When this rough surface is exposed with the peeling of the formed film, the effect of preventing rust is lost. Further, the rough surface makes drastic metal contact with its mating surface, causing drastic abrasion that results in damages such as smearing and seizing.
Under these circumstances, the present invention was made. It is an object of the present invention to provide a rolling sliding member, a process for the production thereof and a rolling sliding unit such as rolling bearing for bearing roll neck, which has a sufficient durability capable of enduring severe conditions during use.
Among the rolling sliding member of the invention, process for the production thereof and sliding unit, the rolling sliding member is made of an iron-based metal and has a surface roughness of 1.2 xcexcm or less as calculated in terms of Ra or 12 xcexcm or less as calculated in terms of Rmax at least on the area thereof which comes in contact with the surface of its mating member with relative displacement during use.
The process for the production of a rolling sliding member comprises forming a formed film at least on the area of an iron-based metal which comes in contact with the surface of its mating member with relative displacement during use, and then subjecting the formed film to smoothing for lessening the surface roughness thereof.
The rolling sliding member is made of an iron-based metal and has a formed film provided and has been subjected to smoothing for lessening the surface roughness thereof at least on the area thereof which comes in contact with the surface of its mating member with relative displacement during use.
The rolling sliding units each are made of an iron-based metal and comprise a pair of rolling sliding members which make displacement relative to its mating member during use.
In the rolling sliding unit, one of the pair of rolling sliding members has a formed film provided at least on the area thereof which comes in contact with the surface of its mating member with relative displacement during use while the other has no formed film provided but has a surface roughness of 0.1 xcexcm or less as calculated in terms of Ra at least on the area thereof which comes in contact with the surface of its mating member with relative displacement during use.
In the rolling sliding unit, the pair of rolling sliding members have a surface roughness of 0.1 xcexcm or less as calculated in terms of Ra anywhere on the area thereof which comes in contact with the surface of its mating member with relative displacement during use.
Alternatively, though not being defined in the claims, one of the pair of rolling sliding members may have a smoothened formed film provided at least on the area thereof which comes in contact with the surface of its mating member with relative displacement during use while the other may have a formed film provided or may have no formed film provided but have a surface roughness of 0.1 xcexcm or less (preferably 0.07 xcexcm or less) as calculated in terms of Ra at least on the area thereof which comes in contact with the surface of its mating member with relative displacement during use.
(Function)
In accordance with the rolling sliding member of the invention, process for the production thereof and rolling sliding unit having the foregoing constitution, interference with protrusions developed when this rolling sliding member makes movement relative to its mating member or a pair of rolling sliding members constituting this rolling sliding unit make movement relative to each other is lessened. In other words, since the surface roughness of the rolling sliding member or unit is so small that minute protrusions present thereon are small, drastic abrasion can be inhibited, making it possible to prevent early peeling of formed film.
Further, even if a formed film is peeled, the process reaching peeling forms a mild phenomenon (phenomenon gradually proceeds over an extended period of time). Accordingly, the substrate which is an iron-based metal undergoes so-called concordance. In other words, the surface roughness of the substrate is lessened before the foregoing formed film is peeled. Therefore, even after the peeling of the formed film, the substrate has sufficient abrasion resistance and seizing resistance.